1. Field of the Invention
The present invention relates to the field of wireless communications.
2. Description of Related Art
A typical wireless communications network, such as a cellular or a personal communication system (PCS) network, includes three main elements: (1) a mobile telephone switching office (MTSO) which serves as an interface between the wireless network and the public switched telephone network (PSTN); (2) a number of cell cites, or xe2x80x9cbase stations,xe2x80x9d which transmit/receive radio frequency (RF) signals, including control information and traffic, to/from mobile subscriber terminals (xe2x80x9cmobilesxe2x80x9d); and (3) a number of mobiles distributed throughout the geographic region served by the wireless network. Each base station provides service for a sub-area of the network region, and is connected to the MTSO. The MTSO manages channel allocation for each base station, coordinates between moving subscribers and base stations to control handoffs, and controls the operation of establishing connections between mobiles and PSTN terminals.
To allow a mobile subscriber terminal to simultaneously receive and transmit, a typical wireless network uses a first frequency band for forward link communication, i.e., base station to mobile, and a second frequency band for reverse link communication, i.e., mobile to base station. Furthermore, the wireless network typically relies on two types of channelsxe2x80x94traffic channels for carrying voice frequency communication, and control channels for carrying control information used by the MTSO and base stations to establish and monitor call connections and to manage handoffs between base stations as subscribers move through adjacent cells.
When a mobile is switched on, it initially scans a number of forward link set-up channels, such as paging or pilot channels (in Code Division Multiple Access (CDMA) networks), and selects a single forward link set-up channel, normally associated with the nearest base station, based on the relative quality of the channel. When establishing a call connection between a mobile and a PSTN terminal or another mobile, the MTSO assigns a traffic channel to the mobile and instructs the mobile, via the serving base station, the traffic channel which has been assigned. Subsequently, communication between the mobile and the PSTN terminal or other mobile is carried out via the serving base station, the MTSO, and the PSTN (for communication with a PSTN terminal).
Such traffic routing through at least one serving base station and the MTSO occurs even for communication between mobiles which are near one another, thereby tying up network resources, and often resulting in network charges, regardless of the proximity between communicating subscribers.
The present invention is a wireless communications technique which enables a first mobile to directly communicate with a second mobile located within a certain range by executing call set-up and communication functions normally associated with a network base station. The present invention is also a mobile which is equipped to perform like a network base station during a local calling mode to establish and control direct connection between mobiles without contacting a network base station. In this way, the mobile enables local communication without incurring subscriber network charges or tying up network resources.
In one embodiment, a mobile is equipped to reverse transmit and receive frequencies or communication channels during a local calling mode, thereby enabling the mobile to transmit/receive control information and carry out a call with a locally positioned mobile as if it were a base station. In one implementation, the mobile executes a communication channel or frequency sweep operation to identify an idle traffic channel, and thereby minimize interference. When establishing a connection with a local mobile, the mobile pages the local mobile over the forward link set-up channel designated for the base station serving the local mobile, to which the local mobile responds over a reverse link set-up channel (e.g., an access channel). After selecting an appropriate traffic channel, the mobile informs the local mobile of the selected traffic channel via the forward link set-up channel, thereby prompting the local mobile to tune to the designated traffic channel. After successfully establishing the call connection, the mobile transmits a data message over the traffic channel to alert the local mobile user of an incoming call. When the local mobile answers by going xe2x80x9coff-hook,xe2x80x9d a talking connection is established between the mobiles.
In one implementation, the mobile monitors call quality, selects a new traffic channel when call quality drops below a certain threshold, for example based on signal-to-noise ratio or bit error rate, and instructs the local mobile of the new traffic channel via the control channel. Thus, the mobile sets up and carries out a call between local parties without contacting the network base station.